First, roast your hazelnuts. Preheat oven to 350° Fahrenheit. Spread whole, unsalted hazelnuts on a cookie sheet and pop in the oven for 15-20 minutes until the outer skin peels away a bit. Remove and pour into a kitchen towel. Let cool a few minutes, then vigorously rub towel so that some of the hazelnut skins are removed, then let cool completely. Once the nuts are cool, blitz up in a food processor in small batches (1/2 cup MAX per blitzing round or else you'll end up with hazelnut butter) or nutribullet until you have roasted hazelnut flour. (make sure to pick out large pieces that didn't get ground up after each batch)
Then, make the cookie dough! In a large bowl, using an electric mixer, beat together the eggs, sugar, canola oil, and vanilla until thick and lighter. Then mix in the gluten free flour, xanthan gum, hazelnut flour, cornstarch/cornflour, baking powder, and salt until combined. The dough will be very thick but shouldn't be sticky to the touch (if it feels very sticky, add a bit more flour and mix). Then scoop it all into a small bowl cover and chill in fridge for at least 4 hours or overnight.
Once the dough is chilled, preheat oven to 350° Fahrenheit/180 Celcius. Line two cookie sheets with parchment paper. Using a small spoon, scoop out dough and roll into 1.5 inch balls and then press 4-5 chocolate chips into the center of each ball and re-roll so that chocolate chips are inside. Roll balls in powdered sugar and completely coat, then place 2-3 inches apart on the cookie sheets. Bake for 11-13 minutes depending on your oven (I recommend using an oven thermometer to ensure you're at the right temperature!). Do not flatten cookies, they will spread! Let cool slightly, then enjoy!